Where is a transponder installed in an aircraft?

A transponder is a crucial piece of equipment in an aircraft that is primarily responsible for transmitting information about the aircraft's identity and altitude to air traffic control. Its installation location is important for optimal performance and safety.

Typically, the transponder is found in the avionics bay, which is a designated compartment in the aircraft that houses essential electronic equipment such as navigation systems, communication radios, and of course, transponders. This compartment is often designed with considerations for efficient cooling, electromagnetic shielding, and accessibility for maintenance.

Other locations mentioned in the choices are not suitable for transponder installation. The cockpit is primarily reserved for pilot controls and displays, while the engine compartment is focused on engine-related components. The fuselage, while it does house various systems, is not the designated area for avionics. Hence, the avionics bay is the correct and most logical location for transponder installation, ensuring proper functionality and safety in aircraft operations.